1. Field of the Invention
This invention generally relates to a wheel alignment measuring method and system, and, in particular, to a method and system for measuring wheel alignment characteristics of a wheel of a vehicle such as an automobile.
2. Description of the Prior Art
A wheel of a vehicle, such as an automobile, is set with various alignments, such as toe-in and camber angles, and it is important to measure such alignments with high accuracy. In measuring such alignment characteristics of a wheel of a vehicle, there are basically two categories of measuring technologies, i.e., the contact type measuring technology and the non-contact type measuring technology.
In the contact type measuring technology, a measuring apparatus is brought into direct contact with a wheel to be measured for measuring toe-in and camber angles. The contact type measuring apparatus tends to be inexpensive, but its measuring accuracy is limited and difficulty is often encountered in taking measurements for various reasons.
On the other hand, in the case of the non-contact type measuring technology, it is typically based on the triangulation and a rather complicated calculation is required in processing an image of a wheel obtained by a CCD imaging device. An example the non-contact type wheel alignment measuring technology was proposed by one of the present inventors and described in the Japanese Pat. Laid-open Pub. No. 9-280843, assigned to the assignee of this application. As a result, the structure of the non-contact type measuring apparatus tends to be complicated in structure and thus difficulty is encountered in manufacturing the apparatus. Thus, the non-contact type measuring apparatus tends to be expensive.
In accordance with one aspect of the present invention, there is provided a method for measuring an alignment characteristic of a vehicle, comprising:
(a) projecting a first pair of light beams, which are in parallel to each other and separated by a predetermined distance, to a first area of a side wall of a tire of said wheel or to a flat surface detachably attached to said wheel;
(b) receiving reflected light from said first projected pair of light beams incident on said side wall or said flat surface and forming images from said reflected light at an image-forming surface of a first photo-electric converting device at a first location, said first photo-electric converting device being at a fixed distance from said wheel in an approximately axial direction;
(c) measuring a length of a first space between said images formed on said first photo-electric converting device;
(d) calculating a first distance to a first point on said side wall or said flat surface between the points of incidence of said first pair of light beams on said side wall or to said flat detector plate from said first photo-electric converting device, using said length of said first space;
(a2) projecting a second pair of light beams, which are in parallel to each other and separated by a predetermined distance, to a second area of said side wall of a tire of said wheel or to said flat surface detachably attached to said wheel;
(b2) receiving reflected light from said second projected pair of light beams incident on said side wall or said flat surface and forming images from said reflected light at an image-forming surface of a second photo-electric converting device at a second location, said second imaging device being at a fixed distance from said wheel in an approximately axial direction;
(c2) measuring a length of a second space between said images formed on said second photo-electric converting device;
(d2) calculating a second distance to a second point on said side wall or said flat surface between the points of incidence of said second pair of light beams on said side wall or said flat surface from said second photo-electric converting device, using said length of said second space; and
(e) calculating an angle of said wheel from said first and said second distances and said first and second locations of said first and said second photo-electric converting devices.
Preferably, the alignment characteristic is selected from the group essentially consisting of a toe-in angle and a camber angle. When the toe-in angle is selected as an alignment characteristic to be measured, the at least two different measuring locations include at least two locations which are set substantially along a horizontal line on the outer side surface of the tire, which horizontal line is defined by a horizontal plane extending along the axis of rotation of the wheel. Alternatively, when the camber angle is to be measured, the at least two different measuring locations include at least two locations which are set substantially along a horizontal line on the outer side surface of the tire, which horizontal line is defined by a horizontal plane extending along the axis of rotation of the wheel, and also at least one location which is set substantially along a vertical line on the outer side surface of the tire, which vertical line is defined by a vertical plane extending along the axis of rotation of the wheel.
Preferably, the step (e) is carried out at the same time for each of the at least two different locations.
In accordance with another aspect of the present invention, there is provided an apparatus for measuring a distance to a surface, the apparatus comprising:
projecting means for projecting a pair of light beams in parallel to each other, while keeping a separation therebetween at a constant, toward said surface;
a photo-electric converting device having an image forming surface, said photo-electric converting device being capable of converting one or more images formed on said image forming surface into an electrical signal indicating the locations of said one or more images on said image-forming surface relative to a reference location on said image forming surface;
image forming means for receiving light from said projected pair of light beams reflected from said surface and forming a pair of images on said image forming surface; and
processing means for processing said electrical signal produced by said photo-electric converting device responsive to said pair of images formed by said image forming means, and capable of measuring an image separation between said images, and to calculate a distance to a portion of said surface between said pair of projected light beams from a predetermined reference point from said image separation.
Preferably, the image forming means includes an optical lens and the predetermined reference point for measurement is set at the center of the optical lens. The optical lens preferably has a fixed focal distance. The photo-electric converting device preferably includes a CCD image sensor having a predetermined number of pixels along a line defined on the image-forming surface having the predetermined reference location at its end.
Preferably, the processing means includes a central processing unit (CPU) for implementing a calculation according to the predetermined formula to determine a distance to a point of interest (measurement point) on the wheel. The processing means also includes means for determining a toe-in angle according to another formula based on at least two distance measurements obtained for at least two different locations of a wheel and also for determining a camber angle according to a further formula based on at least three distance measurements obtained for at least three different locations of a wheel.
In accordance with a further aspect of the invention, there is provided an apparatus for measuring alignment of a wheel of a vehicle, comprising:
a plurality of measurement apparatuses, each of said measuring apparatuses including:
projecting means for projecting a pair of light beams, in parallel to each other while keeping a separation therebetween at constant, toward a side wall of a tire of said wheel or a flat surface detachably attached to said wheel;
a photo-electric converting device having an image forming surface, said photo-electric converting device being capable of converting one or more images formed on said image forming surface into an electrical signal, said signal indicating the locations of said one or more images on said image-forming surface relative to a reference location on said image forming surface;
image forming means for receiving light from said projected pair of light beams reflecting from said side wall or from said flat detector surface, thereby to form a pair of images of said pair of light beams on said image forming surface; and
a reference to said reference location on said image forming surface;
wherein each measuring apparatus has been calibrated to produce a set of calibration data, and
a structure, for positioning each of said plurality of apparatuses in a reference plane at a plurality of locations, each location being at roughly the same radial distance from the axis of rotation of said wheel, and said beams being projected roughly parallel to said axis of rotation; and
processing means for:
processing said electrical signals produced by each of said photo-electric converting devices of each of said plurality of apparatuses;
calculating each of a plurality of distances to a plurality of portions of said side wall or said surface from said references of said plurality of apparatuses from said electrical signals and said set of calibration data; and
calculating at least one alignment angle of said wheel from said plurality of distances so calculated.
Preferably, the first measuring apparatus includes a first pair of light sources for producing the pair of light beams, which are located on the opposite sides of the associated photo-electric converting device while lying in the same horizontal plane. The first pair of light sources preferably projects its pair of light beams toward a top portion of a side wall of a tire of a wheel to be measured or of the flat detector surface of a detector disc detachably attached to the wheel. Also preferably, the second measuring apparatus includes two second pairs of light sources each for producing the pair of light beams, the light sources of each of the second pairs which being located on top and bottom of the associated photo-electric converting device while lying in the same vertical plane. Each of the second pairs of light sources preferably projects its pair of light beams to a location of a side wall of a tire of a wheel to be measured in the vicinity of a horizontal plane extending along the center of rotation of the wheel or of the flat detector surface of a detector disc detachably attached to the wheel.
Preferably, the system further comprises positioning means for positioning each of the first and second measuring apparatuses relative to a wheel to be measured. Preferably, the positioning means includes first positioning means for positioning the first measuring apparatus relative to a wheel to be measured and second positioning means for positioning each of the second measuring apparatuses relative to a wheel to be measured. Preferably, the first positioning means has a function for moving the first measuring apparatus along a vertical direction and setting the first measuring apparatus at a desired height. In addition, the second positioning means has a function for moving each of the second measuring apparatuses along a predetermined slope and setting it at a desired height and horizontal location. These first and second positioning means can be implemented by any positioning mechanisms, such as elevators, which are well known to those skilled in the art.
It is therefore a primary object of the present invention to provide an improved wheel alignment measuring method and apparatus simple in structure and low at manufacturing cost.
Another object of the present invention is to provide a wheel alignment measuring method and apparatus easy, fact and accurate in operation.
A further object of the present invention is to provide an improved non-contact type wheel alignment measuring system compact in structure and easy to manufacture.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.